Diode laser‐assisted transcanal endoscopic removal of an aural polyp in the external auditory canal of a dog

Abstract Background In humans, aural polyps comprise fibrovascular tissue covered by the respiratory epithelium. Aural polyps with ciliated epithelium are common in cats but are rarely reported in dogs. In a previous case, a mass filled the tympanic cavity alone, and it was surgically removed. Objectives To report a case of a canine aural polyp with ciliated epithelium extending from the dorsal tympanic cavity to the external auditory canal with detailed otological features and to demonstrate the usefulness of the transcanal endoscopic procedure (TEP) with a diode laser as a less‐invasive therapy. Methods A 12‐year‐old castrated male Cavalier King Charles Spaniel presented with a 6‐month history of unilateral chronic otorrhoea. Video‐otoscope examination revealed a protruding, reddish and soft‐to‐rubbery round mass in the right horizontal ear canal. Computed tomography and magnetic resonance imaging further revealed a smooth mass extending from the dorsal portion of the tympanic cavity into the horizontal part of the external auditory canal. However, it showed no lesions in the dorsal tympanic cavity. Results The mass was removed using aural forceps by a traction‐torsion manoeuvre. The suspected base of the mass on the caudal side of the upper tympanic cavity was confirmed by a rigid scope, and it was completely vaporised with a diode laser. Histopathology revealed foci of columnar ciliated epithelium embedded in the connective tissue encapsulated by stratified squamous epithelium. No recurrence was observed at 3 years and 8 months. Conclusion We describe a rare case of an aural polyp with ciliated epithelium extending from the upper‐middle ear to the external auditory canal in a dog. The TEP using a diode laser may be a useful minimally invasive treatment option for managing external auditory canal polyps.


INTRODUCTION
A polyp is a macroscopic benign projection from mucosal epithelial surfaces, such as the middle ear, colon, cervix, stomach, nose, uterus and throat (Wilcock, 2007). Aural polyps are histologically confirmed by a core of loosely arranged fibrovascular tissue covered by columnar ciliated epithelium (Wilcock, 2007). They are associated with chronic inflammation in the middle ear, and cholesteatomas are considered one of the aetiological causes in humans (Gliklich et al., 1993;Milroy et al., 1989). The terms 'aural polyp' or 'inflammatory polyp' in the ear can be widely used in veterinary medicine for any fibrovascular tissue projection with or without respiratory epithelium (Wilcock, 2007); polyps originating from the middle ear are commonly seen in cats. However, they are uncommon in dogs (Blutke et al., 2010;Greci & Mortellaro, 2016;Pratschke et al., 2003). There are only two detailed descriptive reports on aural polyp in dogs (Blutke et al., 2010;Pratschke et al., 2003). Blutke et al. (2010) reported the case of a dog with a typical aural polyp, as seen in humans and cats. A polyp filled the middle ear without extending into the external auditory canal. It was histologically confirmed by the presence of the overlying surface layer of the respiratory epithelium. In this case, surgical resection of an aural polyp using ventral bulla osteotomy (VBO) was performed. This approach led to higher morbidity than simple traction; however, it carried a lower risk of recurrence (Greci & Mortellaro 2016). Aural polyps in cats are removed by per-endoscopic trans-tympanic traction as a non-surgical approach (Greci et al., 2014); this is minimally invasive. However, in this instance of simple repeated grasping and pulling to debulk the mass, a portion of the stalk remnant may remain, which increases the risk of polyp recurrence (Greci & Mortellaro, 2016). Herein, we report the case of a dog with an aural polyp comprising of ciliated epithelium that extended from the middle ear to the external auditory canal, where the transcanal endoscopic procedure (TEP) using a diode laser resulted in a successful outcome.  Moreover, it was slightly hyperintense on T1-weighted imaging (T1WI) compared to the grey matter, and it had a hypointense core on all sequences with a suspected artefact on T2* (observed T2WI), consistent with mineralisation. In the contralateral left tympanic cavity, hyperintense material was coincidentally noted on T2WI/FLAIR and T1WI, consistent with high protein fluid suggestive of secretory otitis media ( Figure 3).

Treatment
The mass was removed using 9 cm-long aural forceps (Micro-curette, SHIN-MEDICO Inc., Chiba, Japan) for traction-torsion via the TEP F I G U R E 2 Computed tomography of the skull. (a) A smooth mass is seen in the horizontal external auditory canal in the right ear (asterisk). The distal portion of the mass is homogeneously enhanced. In contrast, the proximal portion is heterogeneously enhanced with partial mineralisation (white arrow). (b) A mass is seen extending from the dorsal portion of the tympanic cavity (white arrowhead) but not into the ventral portion of the tympanic cavity. Coincidentally, the middle ear effusion is seen in the contralateral left tympanic cavity  et al. (2003). In one retrospective study on aural polyps in humans, two categories of polyps were described accordingly: polyps associated with cholesteatoma and those unrelated to cholesteatoma (Milroy et al., 1989). It is assumed that aural inflammatory polyps and polypoid masses are not single entities; as in humans, cholesteatomaassociated polypoid growth is a differential diagnosis of aural polyps in dogs. In the present case, the histopathological evaluation revealed a mass with columnar ciliated epithelium embedded in the connective tissue encapsulated by stratified squamous epithelium. Furthermore, neither CT nor MRI revealed any findings suggestive of cholesteatoma, including bone changes at the contour of the tympanic bulla, osteolysis, osteoproliferation and osteosclerosis, expansion of the tympanic cavity or sclerosis or osteoproliferation of the ipsilateral temporomandibular joint and the paracondylar process (Imai et al., 2019;Travetti et al., 2010). We believe that this is the first description of an aural polyp with ciliated epithelium extending from the upper-middle ear to the external auditory canal in a dog that resembled feline and human cases.
The polyp in the present case had partial central calcification. Similar clinical and histological findings have been reported in human aural polyps (Sogebi, 2012). A few foci of calcification in the polyp were also observed in a previous case in a dog (Blutke et al., 2010). The present case had a 6-month history of otorrhoea. It is suspected that a longstanding inflammatory process in the middle ear led to this pathologic change. The difference in epithelial lining may have reflected differences in aetiology, degree and chronicity of concomitant inflammation, as well as different anatomical sites of origin of aural polyps (Blutke et al., 2010). An aural polyp is considered a non-specific pathological sequela or complication of chronic otitis media in humans; conversely, polyps can also cause otitis media (Gliklich et al., 1993). CKCS is a breed known to be predisposed to primary secretory otitis media; the concurrent otitis media observed in the contralateral tympanic cavity suggests subclinical chronic inflammation in the middle ear.
In the case reported by Blutke et al. (2010), the aural polyp was removed surgically via ventral bulla osteotomy, and other reported canine polyps to date have also been surgically resected similarly.
In contrast, most feline polyps reported have been removed via non-surgical means. Regardless of the approach, postoperative complications can occur (Greci & Mortellaro, 2016). Polyps are clinically benign and rarely life-threatening lesions; therefore, a less-invasive approach should be considered where feasible (Imai et al., 2019).
Traction-avulsion is the simplest means; however, a portion of the stalk may remain, increasing the risk of polyp recurrence (Greci & Mortellaro, 2016). Per-endoscopic trans-tympanic traction using small forceps or curettes can remove the residual portion and reduce the recurrence rate; however, this procedure is time-consuming (Greci et al., 2014). Carbon dioxide laser ablation of polyps is another promising technique for aural polyp removal (Greci & Mortellaro, 2016 (Usui et al., 2015).
In the present case, the base of the polyp was vaporised by the diode laser, and a successful outcome was subsequently obtained.

CONCLUSIONS
A dog had an aural polyp with ciliated epithelium extending from the upper-middle ear to the external auditory canal, which was confirmed by both diagnostic imaging and histopathology. It was successfully removed using transendoscopic traction plus laser ablation of the base without a traditional surgical approach. No recurrence was observed at 3 years and 8 months. TEP using a diode laser seems to be valuable as a less-invasive approach.
No conflicts of interest have been declared.

ETHICS STATEMENT
The authors confirm that the ethical policies of the journal, as noted on the journal's author guidelines page, have been adhered to. No ethical approval was required as this is a retrospective case report with no original research data.

STUDY PRESENTATION
This study has been presented in Asia Meeting of Animal Medicine Specialties in 2019.

DATA AVAILABILITY STATEMENT
Data openly available in a public repository that issues datasets with